Moisture-proof ionization smoke detector

Abstract

An ionization smoke detector of the present invention has an annular engaging flange portion formed integrally on the periphery of an insulating board and an engaging groove formed on a cover, so that a circuitry-accommodating portion may be moisture- and gas-tightly sealed merely by inserting the flange portion into the groove, without using special sealing members such as ruber packing members. In an intermediate electrode mounting structure of the present invention, support legs are formed integrally on the periphery of the intermediate electrode which may be simply inserted into an opening of the insulating board to fix and support the intermediate electrode, without using screws etc. Thus, a space needed to mount the intermediate electrode can be minimized. An electrode lead is connected to a lead of an FET insulatedly potted at an appropriate place on the backside of the insulating board with a hot melt synthetic resin. This can prevent possible penetration of moisture or corrosive gases into the circuitry-accommodating portion by the insulation sealing of the FET, even though the electrode lead passes through an opening of the insulating board. Thus, corrosion of the circuit parts can surely be avoided.

What is claimed is: 
     
       1. A ionization smoke detector, comprising a cover, an insulating board having a backside being provided within said cover, a circuit board disposed on the backside of the insulating board, said insulating board having an inner electrode with a radiation source, an intermediate electrode formed with an opening for transmitting radiation from said radiation source, and an outer electrode formed with smoke inlets on its side wall, said inner, outer and intermediate electrodes mounted on said insulating board;   said insulating board having an annular engaging flange portion formed integrally on a periphery of the insulating board, and said cover having an engaging groove into which said engaging flange is inserted;   said engaging flange having a tip end extending towards the backside of the insulating board and directed outwardly; and   said engaging groove having an outer inside wall inclined so that the engaging flange inserted into the groove presses against the wall.   
     
     
       2. An ionization smoke detector, comprising a cover, an insulating board provided within the cover and having a foreside and a backside, a circuit board disposed on the backside of the insulating board, said insulating board having an inner electrode with a radiation source, an intermediate electrode formed with an opening for transmitting radiation from said radiation source, and an outer electrode formed with smoke inlets located within a side wall thereof, said inner, outer and intermediate electrodes being mounted on said insulating board;   said intermediate electrode having a plurality of supported legs and at least one electrode lead formed integrally with one of said legs;   said electrode lead being inserted into a slit from the foreside of the insulating board and connected to a lead of an FET incorporated and insulatedly sealed on the backside of the insulating board; and   each said support leg having serrated edges being inserted and fixed in holes provided within the foreside of the insulating board.   
     
     
       3. An ionization smoke detector according to claim 2, in which said electrode lead is formed integrally with the support leg in the form of extension of the support leg. 
     
     
       4. An ionization smoke detector according to claim 2, in which said insulating board has openings for passing contact metal members of the outer electrode for the circuit board therethrough, said openings being formed, leaving a thin, film-like portion before the contact metal members have been passed therethrough. 
     
     
       5. An ionization smoke detector according to claim 2, in which said insulating board has an opening for inserting a LED on the circuit board for alarm indication therethrough, said opening being formed, leaving a thin, film-like portion before the LED has been inserted therethrough. 
     
     
       6. An ionization smoke detector according to claim 2, in which said inner electrode has a shoulder portion and said insulating board has an opening for fitting the inner electrode, said inner electrode is caulked at said shoulder portion to be fixed in place after it has been fitted in the opening of the insulating board. 
     
     
       7. An ionization smoke detector, comprising a cover, an insulating board provided with the cover and having a foreside and a backside, a circuit board disposed on the backside of the insulating board, said insulating board having an inner electrode with a radiation source, an intermediate electrode formed with an opening for transmitting radiation from said radiation source, and an outer electrode formed with smoke inlets located within a side wall thereof, said inner, outer and intermediate electrodes being mounted on said insulating board;   said insulating board having an annular engaging flange portion formed integrally on a periphery of the insulating board, and said cover having an engaging groove into which said engaging flange is inserted;   said engaging flange having a tip end extending towards the backside of the insulating board and directed outwardly;   said engaging groove having an outer inside wall inclined so that the engaging flange insert into the groove presses against the wall;   said intermediate electrode having a plurality of support legs and at least one electrode lead formed integrally with one of said legs;   said electrode lead being inserted into a slit from the foreside of the insulating board and connected to a lead of an FET incorporated and insulatedly sealed on the backside of the insulating board; and   holes being provided within the foreside of the insulating board, said support legs each having serrated edges for inserting and fixing within said holes.